Cold hobbable steel



Patented Sept. 21, 1948 Maurice C. Fetzer, Wyomissing, and William H.

Kemper, Temple, Pa., assignors to The Carpenter Steel Company, Reading, Pa., a corporation of New Jersey No Drawing. Application June 12, 1945, Serial No. 599,120

This invention relates to alloy steels particularly adapted for making cold hobbed articles.

An object of the invention is toproduce alloy steels having unique combinations of properties including cold hbbbability, low annealed hardness, ability to harden by both air cooling and oil quenching and in respect not only of the core but also of the case obtainable by case hardening, hot hardness of the core and the case, and stability of surface hardness of the case' at temperatures up to about 1000 F., as well as toughness of the case and core when properly drawn and improved abrasion resistance particularly at high temperatures.

An alloy steel having the above mentioned combination of properties has particular value in the manufacture of-cold hobbed articles, e. g., molds and mold parts, for example, those used in the molding of plastics and plastic compositions requiring high molding temperatures; e. g., of the order of 500 F. to 800 F. Many of these compositions contain abrasive fillers which emphasize the need for a steel which will develop an abrasion resistant surface and will possess relative stability of surface hardness and abrasion resistance at relatively high molding temperatures,

There are available a number of irons and alloy steels which possess cold hobbability ,but are deficient in 'one or more of the above mentioned other properties. There are also a number of alloys which possess desirable degrees of hardness and ability to harden when air cooled or oil quenched as well as hot hardness, but are deficient in hobbability and therefore require thatthe mold cavity be machined. In other words, the experience in the art has been that the attainment of desirable properties such as high cold and hot hardness and ability to harden in air oroil is accompanied by lack of hobbability, and conversely that the property of hobbability is secured at the sacrifice of other desirable properties such as cold and hot hardness and ability to harden.

The advantages and objects of the invention will be further described as follows:

The steel alloys of this invention can be annealed to 125 maximum Brinell and therefore are easy to cold hob. After forming, the alloys can be hardened by heat treatment. Hardnesses of to 43 Re are obtainable. The hardness referred to may be produced by air cooling without resorting to oil or water quenching although the alloys may be hardened by oil quenching. High strength accompanies the high hardness and persists at elevated temperatures and all of V 3 Claims. (Cl. 75.12.6)

the above properties are obtained without unduly sacrificing toughness. When carburized by known methods the alloys develop a case of normal depth which can be hardened to 66 Re, by air cooling directly from the carburizing pack, thus eliminating the necessity of subsequent hardening treatment. The case also has better than ordinary resistance to corrosion, scalingand abrasion at elevated temperatures and the ability to retain its hardness at these temperatures. i All of these properties of the carburized case areobtainable without unduly sacrificing toughness.

The invention will be defined in the claims and the principles thereof will be illustrated in Table I below by examples showing the analyses of certain preferred embodiments of the steel of. the invention as follows: 1

Table I I Examples". 1

010/025. Chromium 4.75/ .00 Molybdenum.

Carbon "I Substana tiall y the. balance.

Substant i a l 1 y the balthe balance.

The properties of the alloy steels produced in accordance with the above examples are shown in subjoinedTable II.

Hobbability, one of the most important. prop: erties, isshown to some extent by the annealed Brinell hardness and to a more significant extent by. what may be termed a hobbability index. This index is a measure of the depth of impression made in the metal by a hob t? in diameter under a load of .30 tons applied for 30 seconds after annealing (slow cooling) from 1600 F, and may be expressed in inches. The greater the depth in inches the more easily is the steel hobbed.

A high heat treated core hardness is desirable because the core supports the case and prevents sinking. Where the steel is used without being carburized the high hardness is an index of the resistance to deformation and abrasion at the temperature of use.

In all the above examples the proportion of chromium may be 4 to 10 per cent instead of the narrower range shown without departing appreciably from the properties given in Table II.

Example 2 Example 3 Hobbability Index'As a'nnealedifrom 1600 F .4 Annealed Hardness (Brinell) As slow cooled from 1600 F. Core Hardnessil Quenched from 1700/1900 F. Core Hardness-Air Cooled from 1700/1900 F Case Hardness 1 Oil uenched from 1700/1900 F Case Hardness 1 Air ooled from 1700/1900 Fl. Hot Hardness of core at 800 F-Brine1l after oil or airha'rdehin'g from 1700l1900 F. Hardness of Case 1 after hardening from 1700/1900'F. and-drawing one hour at 800? F. n V

50 R., (oiltharden- 55 Bo (oil or' air 57 RB (oil or air .,hardenin'g).

hardening) 56 Rs (011 or air hardening).

1 The carburizing treatment consisted of 6 hrs. at 1700 F. in a commercial carburizing compound. The higher the case hardness at. anygiven temperature the greater the resistance'to wear, ab1'a1-- sion and indentation at that temperature.

The above table shows hardness values'for the case as well as the core at ordinary or room temperaturestafter treating and also of the coreat 800 F. The :hot hardness of the case isin'dicated byzthehighhardnessof the'case after "it has been" drawn at 800 F.

. lt willbeseen thatallofthealloysof the above exampleshave in: combination a number of desi-r'aible properties. The' alloys of EXample'Z, containing molybdenum or tungsten; within the specified rangesyhave-distinct advantages over Example 1* in that they'zprovidea high case hard-- nessSby airtreating, (air cooling) and therefore mayo-be air treated directly from the pack. They also have-a somewhat higher hot hardness of the caseas indicated by the drawn. hardness value ofi 55Reuasxcomparedwith'50: Re ofthe alloys of Example 1. Thevalloysof Examples 3 and 4: containing vanadium in the; proportions specified have properties similar. to those of Example 2 except that the drawn hardness is somewhat higher. analysis.

All of the alloysare shown to have a high degreen-ofl-hobbability notwithstanding the attain mentjof the other desirable properties. The addition of 1.5' to 2.5 per cent by weight of cobalt to any of the alloys of Examples 1 to 4 has the added advantage that ."the cobalt lowers the amount. of carbon which is picked up during. carburizing.

1; A cold hobbabl-e steel containing carbon about 0.05 to 0.15 per cent, manganese about 0.10'

to 1;0'0'"per'cent, s'ilicon'about 010150 025' percent, chromium" about' 4100 to 10.00 percent, Vanadium up to 0.50 .;per cent, a metal selected from the group consisting'of molybdenum and'tungstenin the proportion of about 0.90 to 3.0 per cent molybdenum andabout 1.5t0 3.0 per cent tungsten and thebalahcesubstantially iron, said steel having aRockwell C' l'iardriess of about -43 when air cooled from 17 001900 F., a hot hardness of about 82'5 -360Brinel1 at 800"F., after air cooling from 1700 1900 F., and when case hardened providing a. case having a Rockwell C' hardness of about 60765 when aircooled'from 1700 -1900 F.

2'. A cold hobbable steel containing carbon about'0'.05 tof0115 per cent, manganese about 0.10

Example 4 represents the preferred to 1.00 per cent, silicon about 0.10 to 0.25 per cent,

{chromium about 4.00 to 10.00 per cent, vanadium about 0.20to 0.50 per cent and a metal selected from" the group consisting of molybdenum and tungsten in the proportion of about 0.9 to 3.0 per cent-molybdenumand about 1.5 to 3.0 percent tungsten and't-heba'la-nce substantially :iron, said steel havinga Rockwell C hardness of about 25413 when air cooleclrfrorn 1 700 F.-1900 hothardness of -about 335: to 37.0 Brinell at'800" F. after air cooling from'17001900*F. and when case hardenedproviding-a case having a Rockwell C hardness-of a'bout -65 when: .air cooled" from 17001900 'F. and about 57' when the hardened casc 'is drawn 'a't 8001F.

'3; A cold hobbable steel" containing carbon about*0;07- to 0:11 per cent, manganese about 0.20 to 0:50 pericent, silicon about 0.15 to 0z25 per cent, chromium about 4.00 to 10.00 percent. vanadium about 0.20 to 0130; percent, about; 0.90 to 1.30 per cent molybdenum and the balance substantially iron; said steel'having a" Rockwell C hardnessrof about J38' whenair cooled from 1700-F.1900" F., a'hot hardness of about 350Brine1l at 800 after 'aircooling; from-1700-1'900'F." and when case hardenedproviding a case having a Rockwell C hardness ofz-about 64- when-air cooled from 1700" 'F'..1'900.2 aridaabout- '56 when thehardened'.='case:is drawmat'f800fF. 1

, I MAURIE= C; v

i REFERENCES GI'TED The followingreferences fileof'this patent:

UNITED STATES PATENTS are of record in" the Great Britain" Sept. 16.11937 OTHER REFERENCES 

